1. Field of the Invention
The invention relates to improvements in globe maps used as educational devices for the teaching of geography and astronomy and as furniture objects for lighting and decoration.
More precisely, these improvements relate to a special globe map of the type having means for simulating the illumination of the earth by the sun and for displaying the solar time.
2. Description of the Prior Art
A globe map is a special clock which has been described in many patents. Among them, mention may be made of French Pat. No. 1,425,541 (Dugardin--1964) which sets forth in detail the theoretical problems to be solved but describes an entirely mechanical, complex, expensive design which moreover has the drive outside the globe, thus making it considerably less attractive.
An electromechanical drive within the globe is described in U.S. Pat. No. 3,527,046 (Pawl--1970). In that patent, the means for simulating the lighting of the earth by the sun and for displaying the solar time include, within the translucent wall of the globe, a light source, a transparent hemispherical shell with numbered time zone lines, rotated by a day shaft arranged along the polar axis, a hemispherical screen mounted pivotally on bearings integral with said shell arranged in the plane of the equator and an electrical clockworks coupled with said day shaft and with the input of a reducer with a ratio of 1/365.
Thanks to this arrangement, the hemispherical screen driven by the transparent shell rotates at the rate of one revolution per mean solar day around the axis of the day shaft, thereby simulating the day and night lighting of the earth by the sun, while in the northern part of the illuminated terrestrial hemisphere, the solar time is indicated at all points. In addition, thanks to the 1/365 ratio of the reducer which drives a lug engaged in a circle-arc slot provided in the hemispherical screen, this screen oscillates about its pivot axis so as to cover alternately one polar circle and then the other in accordance with the seasons.
The latter globe clock however exhibits certain drawbacks and in particular the very approximate nature of the simulation of daily and annual movements of the earth, the lack of rigor and the complexity of the linkages used and, finally, the total absence of means for setting the day and time.